The present invention relates generally to a control method and system for improving traction of a driven wheel of a motor vehicle operating on an icy or snow surface.
Winter test data show that the maximum value of longitudinal tire force response during a wide-open-throttle tip-in transient on ice is significantly larger than the force predicted by the tire static curve, indicating that there is significant tire friction potential that is not covered by the tire static curve. Dynamic tire friction potential (DTFP) may be used to design an advanced traction control or antilock brake system (ABS) that provides improved performance when compared with the traditional traction control systems based on the static tire curve.
It has been hypothesized in that dynamic tire friction potential may be used to design advanced traction control systems with significantly improved performance when compared with the traditional traction control systems based on the static tire curve. Since the maximum dynamic friction potential occurs at high rates of applied force, of approximately 10000 N/s, implementation of the advanced traction control system would require very fast and precise generation of the wheel torque.
The peak value of the static tire force that can be reached on an ice surface is typically about 700 N. Experiments have shown that the tire force can be increased up to 2000 N, if a high rate of change of the wheel torque is applied for a vehicle starting from standstill. This finding has led to the development of a traction control strategy that is based on generation of consecutive sequences of high-rate linear rise of applied torque. The strategy can be applied in modern electrical or hybrid electrical vehicles, particularly in those equipped with in-wheel electrical motors.